Monday, June 30, 2014

Homemade Puffed Rice

What do you do with old leftover rice? You know, the stuff that's been in the fridge for over a week and has gone dry and hard. Add water and make congee? But the flavours won't mix as well as rice porridge made from scratch. Turn it into fried rice? If you only have a small amount left over, it's hardly worth the trouble. Arancini? These fried balls are delicious, but ideally made with arborio rice, and you want a good amount of it too. Rice pudding? Great, but you've been meaning to cut back on the sugar.

Well, I've just discovered a new use for your old rice, even when there isn't much there—turn it into puffed rice!

Homemade puffed rice.

I didn't come up with this idea spontaneously. In fact, I wasn't even particularly trying to get rid of old rice. How I got onto this project actually started with a discussion about popcorn.

Initial Thoughts: Popping Corn

Popcorn is made from a type of corn with a hard, waterproof, outer shell and a starchy interior. When heated, the moisture inside wants to turn into steam, and pressure builds up within the hull. The starchy centre gelatinises under the heat and pressure, and turns into an airy foam when the hull finally breaks.

Although most of the popcorn sold in New Zealand is in the snowflake-like "butterfly" shape, we came across the other commercial variety with round "mushroom" shaped kernels while in Korea. It seems these are two different varieties of popcorn, so I was surprised to read that the kernels from a single cob of popcorn may form both butterfly and mushroom flakes.

Kernel sizeSmallerLarger
Optimal moisture before popping13.5-14%13.5-14%
Flake / Shape when popped (images from Wikipedia)Irregular, starburst with wings

Round ball

Texture when poppedLight and fluffyFirm and dense
Popping temperatureLower: from 175°C / 347°F, or ideally 204-238°C / 400-460°FHigher: 240-260°C / 464-500°F
AdvantagesFills up cinema boxes easily (high volume to weight)Good for flavoured popcorn as the even surface avoids pooling of flavourings; less fragile so easier to transport

I tried to discuss these popcorn varieties with my Korean friends, and they had no idea what I was talking about. They insisted the popcorn in Korea is just like here. Finally, we worked out what the problem was: while we would call both types "popcorn" in English, in Korean the word pabkon (팝콘) refers to the butterfly version only. The round popcorn is known as gangnaengi (강냉이), which also seems to be the North Korean word for "corn". If you can read Korean, you might like to check out this science project comparing the two popcorn varieties.

Goal: Puffed Rice

While I have tried making butterfly popcorn at home, I couldn't be bothered looking for mushroom kernels for me to play with. Plus, with the higher temperatures needed, it sounded like it would be impossible to cook them with butter without burning. Instead, I thought about what else could be expanded into a delicious snack. Apparently, many grains can be puffed, from amaranth to barley to oats to wheat. What I had on hand at home, however, was rice.

Unlike popcorn, rice doesn't come with a hard, waterproof husk to hold the moisture in and build up pressure. Raw rice you purchase from the shops also does not have enough moisture. If you attempted to heat rice the same way you do popcorn, chances are you will end up with burnt rice.

I decided to do some research and find out how other people puff their rice. As you will see below, there are differences not just in what processes are used, but also in the selection of the rice type. I also learnt some new terminology, for instance:
  • there is a difference between puffed rice (made from cooked or parboiled rice) and popped rice (made from raw rice)
  • paddy is the term for unmilled rice as threshed from the grass, with husk and bran; it is also known as rough rice
  • glutinous or sticky rice is also known as waxy rice
  • glutinous rice doesn't actually contain dietary gluten
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Puffed Rice in India

I was totally amazed by the videos I found of puffed rice makers in India. From what I could see, skilled workers threw unmilled rice into a wok-shaped cooking pot filled with hot sand, and stirred until the grains puff from the heat. They scooped the contents out of the pot, shaking the sand out through a sieve, and that was pretty much it! They make it look so easy!

Sanjeev Kumar says the rice is cooked over low heat in iron kadais, but the temperature can't be that low, as the rice puffs in just a couple of seconds. There also seem to be variations as to how the rice is expanded: some say raw rice is used, completely dried in the husk, sometimes mixed with oil; others say the rice is soaked in salt water first, then either drained or dried. In one video, it looked like the rice was soaked and cooked first, with steam rising from the covered mounds. Other ingredients may also be added to make a delicious street snack.

If you know the Odia language, perhaps you can translate what they are saying in this video filmed in the Tangar Pada village? In the state of Odisha (formerly known as Orissa), where this was filmed, and in particularly in the district of Mayurbhanj, puffed rice is apparently such a significant part of the diet that Geographical Indications (GI) registration was sought.

In Assam, they have a specialty called hurum, which is made from glutinous rice.

Puffed RicePuffed Glutinous Rice
NameMurmura (Hindi),
Muri (Assamese, Bengali),
Mudhi (Odia),Pori (Tamil, Malayalam)
Hurum (Assamese)
Rice usedNon-waxy, e.g.
Waxy (glutinous or sticky) rice, known as bora, e.g.
  • specially-grown local rice variety called borbora
ProcessAccording to the TamilNadu Agricultural University:
"In the traditional process, the paddy is soaked in water preferably over night until saturation, drained and then either steamed or dry roasted in sand for parboiling. The parboiled paddy is milled, salted and again roasted in sand for expansion."
According to a villager who makes this:
"Paddy is first softened in water and subsequently steamed and heated. After the frying process, paddy is broken down by dheki, to separate rice from paddy. Thereafter, it is heated again with sand to get the crunchy product. The finished hurum is immediately sealed in polythene packs to avoid moisture from damaging it"
Texture when poppedLight and crispCrispier, larger and lighter

Obviously, apart from making puffed rice from traditional methods, there are also factories that produce this. Sadly, some have been caught burning tyres for fuel, damaging the health of people in the community, as well as the environment.

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Puffed Rice in Vietnam

From the videos I found of puffed rice making in Vietnam, the process used is very similar to that in India. Although everyone filming seemed to be part of a tour group in the Mekong Delta (with commentary available even in foreign languages such as German), the puffed rice producers also work with unmilled rice, and heat it in a wok-shaped cooking vessel with hot sand. The main differences seem to be the use of sticky rice, a larger pan (presumably as this is part of a commercial operation at a candy factory), and the rice is put into sieves hung from the ceiling: first to remove the sand, then to remove the husks from the puffed rice. One video showed the puffed rice being mixed into caramel and cut into squares for packaging as a sweet snack.

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Puffed Rice (Cakes) in China and Elsewhere

According to Echoes from Old China, the Hakka people are famous for the puffed rice cakes, made by steaming glutinous rice, drying it in the sun, and puffing it in hot sand, to make puffed rice cakes for New Year. This treat has also been taken to Hawaii. However, most videos I encountered online showed the use of an old-fashioned pressure cooker, which makes for a spectacular show.

I have seen pictures from 1938 of the Chinese use of a metal "popcorn hammer" or "popcorn cannon" to make popcorn, and some say this may have been invented in the Song Dynasty (960–1279) for puffing rice. The grains are placed in cast-iron cylinder, which is sealed, then turned over a flame to prevent the contents from burning. Pressure builds up inside, and when a certain level is reached, the container is opened with a loud bang, and the puffed cereal spills out into a prepared bag.

This method of popping rice is also used elsewhere in the world, including in Taiwan, in Japan, and in Korea.

There was also a video which seemed different from the rest, in that it looked like the rice was puffed directly in molten sugar, rather than being puffed first before being added.

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Commercial Production

Despite popcorn and puffed rice having been made in Asia for centuries, Alexander P. Anderson is often credited as the inventor of the process for making puffed cereals such as puffed rice, which was introduced to the American public in 1904. It wasn't until 1913, however, when the product was marketed as "the cereal shot from guns", that sales really took off.

The problem with original gun-puffing process was that the cereals had to be popped in batches. In the 1960s, a continuous puffing gun was created, which increased output. Another commercial process, oven puffing, is described in a patent issued to Kellogg.

Puffing Whole Grains

Gun PuffingOven Puffing
Puffing mechanismRice cooked with steam under high pressure, followed by sudden pressure dropRice cooked and partially dried, then tempered, followed by a sudden application of high heat
Increase in volume6-8 times3-4 times
Grains used
  • Rice
  • Corn
Temperature200-260°C / 400-500°F82.2°C / 180°F (tempering)
232.2-301.7°C / 450-575°F or 290-340°C/ 550-650°F (in later stages of baking)
Pressure1,380kPa / 200 psi, about 13.6 times the atmospheric pressure at sea levelAtmospheric
Moisture5-7% (puffed grains)
1-3% (after drying)
25-30% (cooked rice)
18-20% (after drying)
<3% (after baking)


Most puffed snacks today are made using an extruder. Rather than working with whole grains, a dough made from (rice) flour is squeezed through a die under heat and pressure (150-175°C at 5-10kPa). After drying the pieces to the proper moisture level (from 20-24% down to 9-12%), a sudden release of pressure gun-puffs and dries the shaped dough again at the same time, to obtain the final moisture of 1-3%. This process has a number of advantages over gun-puffing whole grains:
  • greater increase in volume
  • higher production rate
  • greater versatility in product shape
  • easier control of product density
Last year, Cornell University announced a new method of making puffed rice by supercritical fluid extrusion.

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Making Puffed Rice at Home

So... I don't have commercial equipment, a small puffing machine, or a fiery pit to work with sand. I decided to go with the frying method instead. Despite a blogger saying you can puff rice with only 1 tsp oil, it seemed safer to deep-fry, since I have actually seen videos of this working. I am also keen to see if using salt instead of sand would work, though I am not sure if my wok would be able to withstand the heat, and would rather see someone else try it first.

I used jasmine rice, as that was what I had at home, and tried several different methods: frying raw rice, soaked rice, cooked rice, and dried cooked rice.

Raw Rice

I can tell you right now, dropping raw rice in hot oil isn't going to work. There is not enough moisture in the grains for the starch to expand. Even after leaving the rice in for much longer than any of the other trials, nothing seemed to happen.

Raw rice before (left) and after frying (right).
Soaked Rice

If lack of moisture is the problem, it only seemed natural to try soaking the rice in water first. I had the rice soaking for several days so the water could hopefully work its way to the middle of each grain. Unfortunately, I did not give time for the outside to dry, so it splattered when it hit the oil. Still, the grains did expand a little, and became translucent with frying. The end result was quite hard though.

Soaked rice before (left) and after frying (right).
Cooked Rice

Cooked rice is nice and soft, and is expanded somewhat already. This batch was sitting in the refrigerator (in an enclosed box) for a couple of weeks or so too, so it was not too wet. The grains puffed a bit on frying, but stuck together in a clump.

 Cooked rice before (left) and after frying (right).
Dried Cooked Rice

Dried cooked rice is what most people recommend using, and this gave by far the best result out of the variants that I tried. I left the it out for around two weeks, so it looked translucent, shrunken and cracked. It only took a few seconds to puff in the hot oil, and each piece remained distinct, rather than sticking together.

 Dried cooked rice before (left) and after frying (right).
Dried cooked rice before frying.

I made the best puffed rice by frying dried cooked rice in hot oil. This was crispy and delicious, though it also sometimes left some chewy bits stuck to your teeth. You'll need to turn it out onto paper towels to remove as much of the oil as possible.

My puffed rice was quite different from the rice bubbles you can buy in the supermarket, which are mixed with sugar, salt, barley malt extract, and added vitamins and minerals.

My homemade puffed rice (left) and Sanitarium Ricies (right).
I'd like to try some other methods of making puffed rice, but I was quite pleased with the results as they were!

This post is part of Our Growing Edge, a monthly blogging event aimed at inspiring us to try new things. This month, it is hosted by Phuong from My Kitchen of Love.
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